The present invention relates to a two-division type of tire forming mold and a pneumatic tire producing method using the two-division type of tire forming mold. More specifically, the present invention relates to a tire forming mold which prevents damages on a rib and a block effectively in spite of a simple structure thereof when the tire is removed from the tire forming mold, and to a pneumatic tire producing method using the tire forming mold.
A two-division type of tire forming mold has heretofore been used in a process of curing a tire. Such a two-division type of tire forming mold includes a molding surface for molding one side of the tire integrally, and has a simple structure. This has brought up an advantage that costs for related facilities are small. However, in the two-division type of tire forming mold, the tire needs to be separated from the mold in the direction of the tire axis in a state where groove forming ribs arranged on a tread forming surface engage with tread portions. For this reason, there may be a case where parts of the ribs and blocks are damaged while the tire is separated from the mold.
FIGS. 7(a) to 7(c) schematically show how to remove the tire from the two-division type of tire forming mold when the tire has been cured by use of the tire forming mold. FIG. 8 shows a state of the rib and block of the tire when the tire is removed from the tire forming mold. In FIG. 7(a), a mold division position X for dividing a lower half 21 and an upper half 22 of the tire forming mold is set at a position higher than the center line L of the tire T. After completion of curing, the upper half 22 of the tire forming mold is displaced upward to open the tire forming mold, as shown in FIG. 7(b). At this time, the tire T remains in the lower half 21 of the tire forming mold, since the mold division position X is set at a position higher than the center line L of the tire T. Subsequently, as shown in FIG. 7(c), the tire T is pushed up in the direction of the tire axis, thereby separating the tire T from the lower half 21 of the mold. Then, the tire T is transferred outward in the direction of the tire diameter. Here, it should be noted that groove forming ribs are formed on the tread forming surfaces respectively of the lower half 21 and the upper half 22 of the tire forming mold. For this reason, when the tire T is separated from the lower half 21 of the tire forming mold, ribs and blocks which have been formed in the tread portions of the tire T are deformed as shown in FIG. 8. The root portions of some of the ribs and blocks to which the largest stress is applied are ripped, and the ribs and blocks are damaged.
In order to prevent such damages on the ribs and blocks, it has been suggested that a plurality of sector molds for forming the tread portions are provided separately from the lower and upper halves of the tire forming mold, and that these sector molds are displaced outward in the direction of the tire diameter when the tire is removed from the tire forming mold (see Japanese Patent Laid-open Official Gazette No. 2001-129831, for example). However, the sectional type of tire forming mold using the sector molds has a disadvantage that the sectional type of tire forming mold increases costs for related facilities to a large extent.
As other measures, change in the tread compound and modification in the shape of the grooves have been proposed. However, in a case where the tread compound is changed and the shape of the grooves is modified, this makes it difficult to achieve performance required for the tire. In addition, processing application has been proposed. Such processing application includes the coating of the inner surface of the tire forming mold with silicone resin, and vapor deposition of fluororesin on the inner surface of the tire forming mold. However, these cases require maintenance services to be performed continuously, since the coated resins do not have sufficient endurance.